This invention provides a spatially discriminating particle detector, more generally, radiation detector, which enables one to microscopically view a specimen while detecting particles or other species of radiation emanating from the specimen. The apparatus provided may include means for limiting detection to particles or radiation emitted from a small area within the field of view. The discussion and description of the invention which follows is for the most part specifically directed to particle detection. However, it will be appreciated that the invention may generally be applied to the detection of other species of radiation. The most immediate application of the invention is in the field of medicine in the detection of radioisotope flow through a microscopically small part of a specimen which is also being viewed. More specifically, the radioisotope can be monitored with the goal of geometrically and temporally tracing, for example, blood flow or lymphatic drainage.
Solid state detectors have previously been placed in small bore needles for the purpose of detecting particles radiating from tissue penetrated by the needle. However, the detection is blind in that the tissue is not under visual observation. Also, means for restricting the particles detected to those radiated from a microscopically small area has not been achieved.
The invention permits the desired visual observation and particle detection through the use of a microscope objective coupled with a particle detector. The objective includes a primary mirror for receiving light directly from the specimen and a secondary mirror positioned to receive light reflected from the primary mirror and to reflect it again for viewing. The particle detector is placed in the optical shadow (alternatively called the optical dead cone or optical dead space) of the secondary mirror and receives particles radiated directly from the specimen. In a particular embodiment, the mirrors and detector are on a single axis and light from the specimen reflected from the secondary mirror may be viewed through an opening in the primary mirror. The apparatus may include wall structure which absorbs the particles but which defines an elongated straight bore for admitting a predetermined portion of particles emitted from the field under observation.